WORK AND POWER

WARM UP1. Which of the liquids in the graduated cylinder

below is the least dense?2. Which is the most dense?3. Estimate the density of Liquid C.4. Calculate the density of a metal block with a

mass of 40 grams and a volume of 5 milliliters.

BRAIN POP: WORK

WHAT IS WORK?

• Work is done when a force causes an object to move in the direction of the force.• The force and the direction of movement must

be parallel• Always involves a transfer of energy

worknot work

• Applying a force doesn’t always mean that work is done.• Example: if you push against a wall for an

hour, and it doesn’t move, you haven’t done work

Example Direction of force

Direction of motion

Doing work?

Pushing a box

Walking with your backpack on

Lifting a bag of groceries

Carrying a bag of groceries

Work = force x distanceForce applied to an object (in newtons)Distance the object moves (in meters)

Work is measured in Joules (like energy)

Path 1: exert less force over a longer distance Path 2: exert more force over a shorter distance

Same amount of work done for each path

EUREKA: WORK

http://www.youtube.com/watch?v=xBnS23U_ao4

Power is how fast work is done.

Unit of measurement: J/s, or the watt

BRAIN POP POWER

Quiz

IS WORK HAPPENING? Lifting a weight a distance of 2 meters

IS WORK HAPPENING? Holding a weight still over your head for 2 hours

WORK, ENERGY, AND POWER IN HOCKEY

http://science360.gov/obj/video/c5be5456-2e39-49a7-8118-218868df89eb/work-energy-power

BUZZER BEATER

1. What is the formula and unit for work?2. What is the formula and unit for power?3. A force of 15 N is exerted over a distance of 6 m. How much work

was done?

A 21 JB 21 NC 90 JD 90 N

4. If 350 J of work was done in 50 s, what was the power output? F 7 WG 70 WH 1,750 WI 17,500 W